1 May 2017

Infants prefer sweet tastes from day one and this preference continues into early childhood. Human breast milk contains the highest concentration of sugars of all mammalian milks and sweet tasting vegetables (e.g., pureed or well-mashed pumpkin, sweet potato, carrot, etc) and fruits (typically pureed) are some of the first weaning foods we give our babies. In nature, a sweet taste generally signals that a food is safe and desirable.

Most fruits that we cultivate and enjoy today are sweet. They are considered a core food group for the simple reason that they are highly nutritious. Depending on the type, they are good sources of a variety of good stuff including vitamins, minerals, fibre and antioxidants.

With a few notable exceptions (avocados, coconuts and olives), fruits are low in fat and high in water and carbohydrate (primarily in the form of sugars). Apart from melons and some tropical fruits, most have a low GI due to their naturally high fibre and fructose content (and acidity in the case of oranges). For these reasons, most fruits are not very energy dense (they don’t provide a lot of kilojoules per gram), so they generally fill you up without contributing to weight gain. Long-term observational studies indicate that people who eat more fruit weigh less and have a smaller waist circumference.

“Sugar” is the dietary villain de jour. Because most fruits are good sources of a variety of sugars (glucose, fructose and sucrose) they have been singled out by some ill-informed zealots as foods to avoid, or at least limit, in the mistaken belief they may be contributing to rising obesity and associated type 2 diabetes rates. This kind of dietary reductionism may unfortunately lead to unintended consequences like scurvy, which we recently saw in Australia for the first time in modern history, due in part to people avoiding fruit.

Putting ill-informed reductionism aside, how likely is it that excessive fruit consumption is responsible for rising obesity rates in Australia? Dietary guidelines in most parts of the world recommend that people enjoy a minimum of 2 serves of fruit each day:

Australia’s most recent national nutrition survey conducted in 2011/12 found that 77% of all Australians aged 19+ years consumed less than 2 serves a day. The same survey found that 62.8% of all Australians were overweight or obese. The numbers don’t add up. Most Australians aren’t eating much fruit at all.

Finally, a recent clinical trial examined the effect of a low fructose (less than 20 g a day) versus “moderate” (50-70 g a day – moderately high by Australian standards) fructose kilojoule-controlled diet in 107 obese American adults over a 6 week period and found that weight loss was 50% higher in the “moderate” fructose group (4.2 kg) compared to the low fructose group (2.8 kg). The authors concluded “the moderate natural fructose diet was rich in natural fruits that contain many beneficial antioxidants. In addition, patients in the very low fructose diet had a higher glycemic index and glycemic load...”

Whichever way you look at it, avoiding fruit makes absolutely no sense at all.

Alan Barclay, PhD is a consultant dietitian. He worked for Diabetes Australia (NSW) from 1998–2014 and is a member of the editorial board of Diabetes Management Journal (Diabetes Australia). He is author/co-author of more than 30 scientific publications, and co-author of The Low GI Diet: Managing Type 2 Diabetes (Hachette Australia) and The Ultimate Guide to Sugars and Sweeteners (The Experiment, New York). You can read a review of his latest book, Reversing Diabetes (Murdoch Books), in Glycosmedia Diabetes News.